The hepatitis C virus is an enveloped, single-stranded, positive sense RNA virus in the family Flaviviridae. HCV mainly replicates within hepatocytes in the liver. Circulating HCV particles bind to receptors on the surfaces of hepatocytes and subsequently enter the cells. Once inside the hepatocyte, HCV utilizes the intracellular machinery necessary to accomplish its own replication. Lindenbach, B. Nature 436(7053):932-8 (2005). The HCV genome is translated to produce a single protein of around 3011 amino acids. This “polyprotein” is then proteolytically processed by viral and cellular proteases to produce three structural (virion-associated) and seven nonstructural (NS) proteins.
HCV encodes two proteases, the NS2 cysteine autoprotease and the NS3-4A serine protease. The NS proteins then recruit the viral genome into an RNA replication complex, which is associated with rearranged cytoplasmic membranes. RNA replication takes places via the viral RNA-dependent RNA polymerase of NS5B, which produces a negative-strand RNA intermediate. The negative strand RNA then serves as a template for the production of new positive-strand viral genomes. Nascent genomes can then be translated, further replicated, or packaged within new virus particles. New virus particles presumably bud into the secretory pathway and are released at the cell surface.
HCV has a high rate of replication with approximately one trillion particles produced each day in an infected individual. Due to lack of proofreading by the HCV RNA polymerase, HCV also has an exceptionally high mutation rate, a factor that may help it elude the host's immune response.
Based on genetic differences between HCV isolates, the hepatitis C virus species is classified into six genotypes (1-6) with several subtypes within each genotype. Subtypes are further broken down into quasispecies based on their genetic diversity. The preponderance and distribution of HCV genotypes varies globally. For example, in North America genotype 1a predominates followed by 1b, 2a, 2b, and 3a. In Europe genotype 1b is predominant followed by 2a, 2b, 2c, and 3a. Genotypes 4 and 5 are found almost exclusively in Africa. Genotype is clinically important in determining potential response to interferon-based therapy and the required duration of such therapy. Genotypes 1 and 4 are less responsive to interferon-based treatment than are the other genotypes (2, 3, 5 and 6). Duration of standard interferon-based therapy for genotypes 1 and 4 is 48 weeks, whereas treatment for genotypes 2 and 3 is completed in 24 weeks.
The World Health Organization estimates that world-wide 170-200 million people (3% of the world's population) are chronically infected with HCV. Approximately 75% of these individuals are chronically infected with detectable HCV RNA in their plasma. These chronic carriers are at risk of developing cirrhosis and/or liver cancer. In studies with a 7-16 years follow-up, 7-16% of the patients developed cirrhosis, 0.7-1.3% developed hepatocellular carcinoma and 1.3-3.7% died of liver-related disease.
The only treatment option available today is the use of interferon α-2 (or its pegylated form) either alone or combined with ribavirin. However, sustained response is only observed in about 40% of the patients and treatment is associated with serious adverse effects. There is thus an urgent need for potent and selective inhibitors of HCV.
Relevant disclosures include U.S. Pat. Nos. 4,914,108; 4,988,707; 4,990,518; 5,137,896; 5,208,242; 5,227,384; 5,302,601; 5,374,638; 5,405,964; 5,438,063; 5,486,525; 6,479,508; and U.S. Patent Publication No. US2003/0108862 A1, Canadian Patent No. 2423800 A1, German Patent Nos. 4211474 A1, 4236026, 4309969, 4318813, European Patent Nos. EP 0 138 552 A2, EP 0 706 795 A2, EP 1 132 381 A1, Great Britain Patent No. 2158440 A, PCT Patent Publication Nos. WO 00/20416, WO 00/39127, WO 00/40583, WO 03/007945 A1, WO 03/010140 A2, WO 03/010141 A2, WO 93/02080, WO 93/14072, WO 96/11192, WO 96/12703, WO 99/27929, PCT-US2004/43112, PCT-BE2003/000117, PCT-US2005/26606, Akamatsu, et al., “New Efficient Route for Solid-Phase Synthesis of Benzimidazole Derivatives”, 4:475-483, J. COMB. CHEM., 2002, Baginski S G et al., Proc. Natl. Acad. Sci. U.S.A. 2000 Jul. 5; 97(14):7981-6). Cleve et al., “Derivate des Imidazo[4.5-b]- and lmidazo[4.5-c]pyridins”, 747:158-171, JUSTUS LIEBIGS ANNALEN DER CHEMICA, 1971, Kiyama, et al., “Synthesis and Evaluation of Novel Nonpeptide Angiotensin II Receptor Antagonists: Imidazo[4,5-c]pyridine Derivatives with an Aromatic Substituent”, 43(3):450-60, CHEM PHARM BULL, 1995, Mederski et al., “Synthesis and Structural Assignment of Some N-substituted Imidazopyridine Derivatives”, 48(48):10549-58, TETRAHEDRON, 1992, Yutilov et al., 23(1):56-9, KHIMIKO-FARMATSEVTICHESKII ZHURNAL, 1989. In addition, see WO 05/063744.
A need exists for compounds having desired anti-HCV therapeutic and/or prophylactic attributes, including high potency, selectivity and oral bioavailability (suitable for administration once or twice a day), low toxicity (including acceptable performance in the hERG patch clamp assay, absence of pulmonary permeability edema and no effect on QT interval), minimal or no metabolic activation/glutathione adduct formation, no evidence of genotoxicity, low metabolic turnover and low plasma clearance, wide-spectrum efficacy against HCV genotypes (especially 1a and 1b, 2 , 3 and 4), efficacy against HCV resistance mutations (limited overlap in resistance profiles with other non-nucleoside NS5B inhibitors in clinical trials), and compatibility with other HCV therapeutics such as interferon and ribavirin. The safety profile should permit chronic dosing for periods of at least I year.